In known two-way radio frequency communication networks, a number of transmitter units are used to transmit messages on various frequency channels to portable selective call communication devices such as a two-way pager, cellular telephone, radio, etc. One or more receivers are associated with each transmitter for receiving messages from a portable two-way device. In accordance with one known method for allocating frequency channels as described in U.S. Pat. No. 5,280,630, each base station which includes a transceiver and controller determines the frequency channel to be used to transmit a message using a preferred channel list thereby providing a fully distributed channel allocation scheme wherein each base station can operate independently to carry out this function. The preferred channel list is maintained at each base station of the network wherein the base stations use real time measurements of channel quality and a history of the channel quality to determine the preferred channel list for channel allocation purposes. However, real time measurements of the current channel quality can be costly. Using only statistics of the past history is not satisfactory for channel allocation because such systems merely predict the channel quality and are not based on any real measurements.
Therefore there is a need to provide a channel allocation scheme that provides a balance among the competing factors of channel quality, system capacity, adaptivity, cost, complexity, fairness in terms of equal access, etc. It is noted that although some networks organize transmitters in zones for simulcasting an address of a selective call device, the actual messages are not simulcast to the device by all of the transmitters in the zone. Instead, a central controller determines which individual transmitter in a zone is to be selected for transmitting the actual message. See for example U.S. Pat. Nos. 4,670,906 and 4,918,437. Heretofore, when transmitter units have been grouped in zones, the zones have not been adaptive; nor have they been employed to provide a channel allocation scheme that meets the desired needs.